We propose an entirely new application of new brain imaging technology (Near Infrared Spectroscopy, NIRS) to a previously unresolved scientific debate that has puzzled scientists for nearly 40 years: How do young infants discover the phonetic building blocks of their language from the constantly varying linguistic and perceptual stream around them? NIRS is non-invasive optical technology that, like fMRI, measures cerebral hemodynamic activity and thus permits 1 to "see" inside the brains of children and adults while processing specific aspects of language and cognitive tasks. Unlike fMRI, NIRS is highly portable, child-friendly (child can be seated on mom's lap in home, lab or school), tolerates movement more than fMRI (participants can vocalize/talk), and can be used with alert babies. Standardized behavioral tasks involving (i) visual perception, (ii) auditory perception, and (iii) native and non-native phonetic perception will be used with "young" (3-4 mo) and "old" (13-14 mo) infants and adults during NIRS recordings to test specific within- hemisphere neuroanatomical hypotheses about specific tissue (and networks of neural tissue) and their linguistic or general auditory perception functions. Our use of this exciting new NIRS technology with infants in this way will provide important resolutions to scientific questions about (a) the multiple factors that underlie early language acquisition and general auditory perception and the specific type of processing tissue that govern them, (b) the developmental trajectories of linguistic and general auditory processing tissue, and (c) the peaked sensitivity that linguistic and auditory processing tissue has to certain kinds of input over others in early development. This work will help resolve classic scientific debate about whether language-specific versus perception-general mechanisms initiate/govern early language learning, and lay bare the multiple factors that become integrated in early life to promote later healthy language growth in children. These findings, with our plan to provide guidelines for the principled use of NIRS with infants, may ultimately be used to identify and predict babies at risk for language/sequencing disorders (e.g., dyslexia) even before they babble or utter their first words. These findings about children's phonological capacity will also provide scientific "evidence-based" information vital to word segmentation in successful language learning and reading and will impact U.S. educational policy regarding early language remediation and teaching. [unreadable] [unreadable] [unreadable]